Okay, I looked up the data I have so far and the DNA End Location Number associated with the O' Brien line (High King of Ireland) does not match the DNA End Location Number associated with Bryan (Sir Francis Bryan). They are two separate lines.
Sir Francis Bryan is on chromosome 2 and O' Brien is on chromosome 6 or 12.
Keep in mind that the haplogroup for Sir Francis Bryan may have a fast mutation rate, making it difficult for people who have him as an ancestor to find AT matches.
Research for Sir Francis Bryan found the following descendants and relatives to all match precisely for the same exact end location number on chromosome 2. Not only were these exact matches on chromosome 2, but there are more common ancestors found in the Bryan line than average which gives this line even more credibility. We are usually very lucky to find one or two common ancestors for a line.
John Love Bryan b. 1792, Common Ancestor; Sir Francis Bryan III b. 1630
James Bryant Jr. b. 1686, Common Ancestor; Sir Thomas Bryan II, KT. b. 1464
Parthenia Bryan b. 1793, Common Ancestor, Sir Francis Bryan III b. 1630
Needham Bryan b. 1690, Common Ancestor, William Smith Bryan b. 1599
Sarah Baldwin Bryan b. 1602, Common Ancestor, Sir Francis Bryan m. Joanne Fitzgerald.
Giving the Bryan line additional weight, AT DNA matches have been found for Smythe on chromosome 10 for a specific matching end location number as follows:
Jane Smythes b. 1590, m. Barnard, Common Ancestor: Alice Smith Watson (Ann Bryan Smiths parents are Sir William Smith and Alice Smith Watson) Ann Smith/Smythe Bryan b. 1650 is on the other end of the match.
Mary Jenney (Smythe) b. 1562, HAPLOGROUP YDNA R1b1a2a1a1b
Common Ancestor: John Richard Smythe, Esq., High Sheriff of Essex b. circa 1490-1495. Ann Smith/Smythe Bryan b. 1650 is on the other end of the match.
Ann (Smythe) Tylney b. circa 1625/1626, common ancestor NN. Ann Smith/Smythe Bryan is on the other end of this match. Ann Smythe Tylney is a biological match.
Now the Fitzgerald's because Bryan children do not exist without Joanne Fitzgerald.
Fitzgerald is also found on chromosome 2 with a different "End Location Number".
Lady Alice Fitzgerald b. circa 1466, Common ancestor: Geroid Mór FitzGerald, 8th Earl of Kildare, Joane Fitzgerald, Sir Francis Bryan's Wife is on the other end of this match.
Richard Baron of Burnchurch Fitzgerald, b. 1550, Common ancestor: Maurice FitzGerald, Lord of Lanstephan b. 1100, Joane Fitzgerald, Sir Francis Bryan's Wife is on the other end of this match.
Lady Eleanor Fitzgerald b. circa 1490, Common Ancestor: Geroid Mór FitzGerald, 8th Earl of Kildare, Joane Fitzgerald, Sir Francis Bryan's Wife is on the other end of this match.
O' Brien is found on chromosome 6 and chromosome 12 for a specific end location number. Because both sets of matches claim the same common ancestor, this line is inconclusive. The common ancestor found in both sets of matches is Turlough O Brian. Chromosome 6 matches are older but have more SNPs. Chromosome 12 matches are more recent with an average number of SNPs in relation to the cM. O' Brien is a very old line which means more variables. For now, it is not confirmed. However neither the chromosome 6 or chromosome 12 matches for O' Brien match Bryan. They are distinctly different.