The sons of Rhodri Mawr continue their Y-chromosome into South Wales. Rhys ap Twedwr Mawr, King of South Wales A.D. 1077, is given in Burke as being derived from Cadelh, King of South Wales. This Cadelh is given as the second son of Rhodri Mawr. [Descent from first son given last post.]
Rhys ap Tewdwr is given as the "Founder of the II. Royal Tribe". The arms are given:
"Gu. a lion ramp. within a bordure indented or."
This would be that the color of the shield is red [ Gu. = Gules = red].
The charge [ordinaries] is a lion standing erect on the hind legs.
The boarder of the shield would be colored gold with its inter margins being jagged or irregular.
From: The General Armory of England, Scotland, Ireland and Wales; Comprising A Registry of Armorial Bearings From The Earliest To The Present Time. By Bernard Burke, published 1884, by Harrison, 59, Pall Mall, London. [p. lxi]
A good reference for South Wales is:
By Ruth Thomas, it was first published in 1977 by John Bartholomew & Son Limited, Edinburgh.