Bleddyn

Since the pronunciation key says DH, I'd assume it's the same sound as Ð in Icelandic, as that's usually either written as DH or TH (TH as in Though, Thou, That).

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Edit: Hearing the pronunciation on Forvo, it does sound exactly like what I said above.
https://no.forvo.com/word/bleddyn/#cy

It doesn't have "bled" in it, it's pronounced "Bleth" as two d's in Welsh make something similar to a TH sound.

Pronounced Blethin, the 'dd' is a 'th' and the 'y' a quick sound.