Sir Sionyn was a famous, merciful and valorous vassal knight noted for his size, oratory skill, and honor.
He was married to Lady Gwenevak who died in 502.
In 481 the couple had a son, Gwanon. The childbirth was not without complications. Gwanon died at the age of seven.
Sir Sionyn adopted Mari who came to inherit him when he died raiding Saxons in 507.
In his last year, Sir Sionyn had the young Count Robert as his squire.